The present invention relates to a composite beam of polygonal cross-section comprising wooden external walls and a core of a material providing the beam with its mechanical strength.
Composite beams are known which are comprised of a hollow metal shape faced on the external surfaces with wood trim (see German Patent No. 30 41 585). This composite system has only the mechanical strength of its internal shape, the wooden elements being necessary mainly for esthetic reasons. Furthermore, there are always empty spaces remaining at the corners which permit the accumulation of dust.
U.S. Pat. No. 250,878 concerns composite beams comprising a wooden frame formed of particle board panels surrounding a space of square cross-section filled with polyurethane foam which is intended to bond together the panel assembly, rigidify the structure and prevent the penetration of humidity into the hollow space present between the panels. Such beams have, at most, the mechanical strength of solid wood beams but do not have the esthetic qualities of the latter.
There are also known quadrangular hollow beams according to German Publication No. P 29 31 162.4-25, which comprise metal external walls assembled from four external elements, with the internal space subsequently filled with concrete and with a plurality of hooks welded to the inside of the walls to provide a strong bond between the concrete and the external panels. Beams of this type are very strong mechanically, but do not have the esthetic quality of wood.
An object of the present invention is to provide a high strength composite beam formed of external wood parts having an excellent appearance.